The present invention relates to a surge absorbing element connected between wires or between a wire and ground in order to protect the electronic circuit of an electronic device from surges such as overvoltages that enter via power supply lines, via communication lines, or the like.
Referring to FIG. 42, there is shown a configuration for a conventional surge absorbing element. A surge absorbing element 72 is connected between lines L1, L2 or between lines L1, L2 and ground. Lines L1, L2 are power-supply lines, communication lines, or the like connected to an electronic circuit 70 of an electronic device. Surge absorbing element 72 protects electronic circuit 70 from lightning surges and the like.
When a surge voltage that exceeds the rating of surge absorbing element 72 is applied between lines L1, L2 or between lines L1, L2 and ground, the surge voltage is conducted through surge absorbing element 72, thus protecting electronic circuit 70.
Surge absorbing element 72 can comprise a gas arrester that uses discharging in a discharge gap, a varistor that has non-linear voltage properties, or the like. Responsiveness is the most important property for reliably protecting electronic circuit 70 from surges.
Currently, one of the most responsive surge absorbers is the silicon surge absorber, which takes advantage of the avalanche effect in pn-junction semiconductors.
However, in practical terms, many silicon surge absorbers have relatively large electrostatic capacities on the order of 2000-5000 pF. This problem is unique to elements that use pn-junction structures. Silicon surge absorbers have electrostatic capacities that correspond to the size of the depletion layer.
For this reason, when such an element is connected to a communication circuit through which high-frequency signals are sent, the impedance is lowered and current leakage is increased. This results in the signal being bypassed via the silicon surge absorber.
Another disadvantage of silicon surge absorbers is that their operating voltage (voltage rating) must be set within a relatively narrow range of around ten volts to several hundred volts per unit.
For this reason, obtaining a relatively high operating voltage requires a plurality of elements connected in series, thus making the overall configuration larger and more complex.